import sys, pygame
from bullet import Bullet
from alien import Alien
from time import sleep


def check_aliens_bottom(ai_settings, stats, screen, ship, bullets):
	'''检查是否有外星人到达了屏幕低端'''
	screen_rect = screen.get_rect()
	for alien in aliens.sprites():
		if alien.rect.bottom >= screen_rect.bottom:
			ship_hit(ai_settings, stats, screen, ship, aliens, bullets)
			break





def ship_hit(ai_settings, stats, screen, ship, aliens, bullets):
	'''响应被外星人撞到的飞船'''
	# 将 ships_left 减 1
	if stats.ships_left > 0:
		stats.ships_left -= 1

		# 清空外星人列表和子弹列表
		aliens.empty()
		bullets.empty()

		# 创建一群新的外星人，并将飞船放到屏幕低端中央
		create_fleet(ai_settings, screen, ship, aliens)
		ship.center_ship()

		# 暂停
		sleep(0.5)
	else:
		stats.game_active = False









def check_fleet_edges(ai_settings, aliens):
	'''有外星人到达边缘时采取相应的措施'''
	for alien in aliens.sprites():
		if alien.check_edges():
			change_fleet_direction(ai_settings, aliens)
			break


def change_fleet_direction(ai_settings, aliens):
	'''将整群外星人下移，并改变他们的方向'''
	for alien in aliens.sprites():
		alien.rect.y += ai_settings.fleet_drop_speed
		ai_settings.fleet_direction *= -1


def update_aliens(ai_settings, stats, screen, ship, aliens, bullets):
	'''检查是否有外星人位于屏幕边缘，并更新外星人群中所有外星人的位置'''
	check_fleet_edges(ai_settings, aliens)
	aliens.update()

	# 检测外星人和飞船之间的碰撞
	# if pygame.sprite.spritecollideany(ship, aliens):
	# 	ship_hit(ai_settings, stats, screen, ship, aliens, bullets)

	check_aliens_bottom(ai_settings, stats, screen, ship, aliens, bullets)


def get_number_rows(ai_settings, ship_height, alien_height):
	'''计算屏幕可容纳多少行外星人'''
	available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
	number_rows = int(available_space_y / (2 * alien_height))
	return number_rows


def get_number_aliens_x(ai_settings, alien_width):
	'''计算每行可容纳多少个外星人'''
	available_space_x = ai_settings.screen_width - 2 * alien_width
	number_aliens_x = int(available_space_x / (2 * alien_width))
	return  number_aliens_x



def create_alien(ai_settings, screen, aliens, alien_number, row_number):
	'''创建一个外星人并将其放在当前行'''
	alien = Alien(ai_settings, screen)
	alien_width = alien.rect.width
	alien.x = alien_width + 2 * alien_width * alien_number
	alien.rect.x = alien.x 
	alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
	aliens.add(alien)





def create_fleet(ai_settings, screen, ship, aliens):
	'''创建外星人群'''
	# 创建一个外星人并计算一行可容纳多少个外星人
	# 外星人间距为外星人宽度
	alien = Alien(ai_settings, screen)
	number_aliens_x = get_number_aliens_x(ai_settings, alien.rect.width)
	number_rows = get_number_rows(ai_settings, ship.rect.height, alien.rect.height)

	# 创建外星人群
	for row_number in range(number_rows):
		for alien_number in range(number_aliens_x):
			# 创建外星人并加入当前行
			create_alien(ai_settings, screen, aliens, alien_number, row_number)





def fire_bullet(ai_settings, screen, ship, bullets):
	'''发射子弹：如果没有到达限制就发射一个子弹'''
	# 创建子弹
	if len(bullets) < ai_settings.bullets_allowed:
		new_bullet = Bullet(ai_settings, screen, ship)
		bullets.add(new_bullet)



def update_bullets(ai_settings, screen, ship, aliens, bullets):
	'''更新子弹的位置，并删除已经消失的子弹'''
	# 更新子弹位置
	bullets.update()

	# 删除已经消失的子弹
	for bullet in bullets.copy():
		if bullet.rect.bottom <= 0:
			bullets.remove(bullet)

	# 如果有子弹击中外星人，删除子弹和外星人
	check_bullet_alien_collisions(ai_settings, screen, ship, aliens, bullets)


def check_bullet_alien_collisions(ai_settings, screen, ship, aliens, bullets):
	'''响应子弹和外星人的碰撞'''
	collisions = pygame.sprite.groupcollide(bullets, aliens, True, True)
	if len(aliens) == 0:
		# 删除现有的子弹并新建一群外星人
		bullets.empty()
		create_fleet(ai_settings, screen, ship, aliens)



def check_keydown_events(event, ai_settings, screen, ship, bullets):
	'''响应按键'''
	if event.key == pygame.K_RIGHT:
		ship.moving_right = True
	elif event.key == pygame.K_LEFT:
		ship.moving_left = True

	# 创建一个子弹，并加入到编组中
	elif event.key == pygame.K_SPACE:
		fire_bullet(ai_settings, screen, ship, bullets)
	elif event.key == pygame.K_q:
		sys.exit()



def check_keyup_events(event, ship):
	'''响应松开'''
	if event.key == pygame.K_RIGHT:
		ship.moving_right = False
	elif event.key == pygame.K_LEFT:
		ship.moving_left = False



def check_events(ai_settings, screen, ship, bullets):
	'''响应键盘和鼠标事件'''
	for event in pygame.event.get():
		if event.type == pygame.QUIT:
			sys.exit()		
		elif event.type == pygame.KEYDOWN:
			check_keydown_events(event, ai_settings, screen, ship, bullets)
		elif event.type == pygame.KEYUP:
			check_keyup_events(event, ship)



def update_screen(ai_settings, screen, ship, aliens, bullets):
	'''更新屏幕上的图像，并切换到新屏幕'''
	# 每次循环时都重新绘制屏幕
	screen.fill(ai_settings.bg_color)

	# 在飞船和外星人后面重绘所有子弹
	for bullet in bullets.sprites():
		bullet.draw_bullet()

	ship.blitme()
	aliens.draw(screen)

	# alien.blitme()

	# 让最近绘制的屏幕可见
	pygame.display.flip()





